Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. As technology has progressed, the demand for smaller semiconductor devices with improved performance has increased. As feature densities increase, the widths of the conductive lines, and the spacing between the conductive lines of back-end of line (BEOL) interconnect structures also need to scale smaller. In addition, other conductive features such as, for example, metal contacts (usually referred as M0) also need to be scaled accordingly.
A move is being made away from the traditional materials used in the past in semiconductor device designs, in order to meet these demands. To reduce the RC time delay, low dielectric constant (low-k) materials are being used as insulating materials, and there is a switch being made to the use of copper for interconnect materials, rather than aluminum. Advantages of using copper for semiconductor device interconnects include abilities to operate faster and manufacture thinner conductive lines because copper has lower resistivity and increased electromigration resistance compared to aluminum. Combining copper interconnects with low-k dielectric materials increases interconnect speed by reducing the RC time delay, for example.
Copper interconnects are often formed using damascene processes rather than by direct etching. Damascene processes are typically either single or dual damascene, which includes forming openings by patterning and etching inter-metal dielectric (IMD) layers and filling the openings with copper. Because copper diffuses easily into some dielectric materials, especially some types of low-k dielectric materials, a diffusion barrier layer is usually deposited on the inner walls of the damascene opening before the copper is formed. Refractory metals such as tantalum (Ta) or titanium (Ti), or nitride compounds of these metals are used as materials of the diffusion barrier layer. However, there are some challenges in using refractory metals in the copper damascene structure since these metallic films have high resistance, thereby causing increased resistance in the copper lines and increased RC delay, especially in small, narrow features.
As the shrinkage of copper lines has progressed in recent years, there is a trend towards thinner films being used for the diffusion barrier layer. Physical vapor deposition (PVD) process used for depositing a thinner TaN/Ta barrier layer encounters difficulties in advanced scale of interconnection. Atomic layer deposition (ALD) process is the candidate to deposit a very thin diffusion barrier layer with uniform coverage, but the ALD method is disadvantageous in extremely low deposition rate and poor throughput. In addition, in manufacturing the TaN/Ta film, a problem occurs in which favorable adhesion between diffusion barrier layer and the IMD layer cannot be achieved. For example, copper lines peel off at the interface, worsening the yield of the semiconductor device.